This invention relates to a load-bearing side web non-pneumatic tire ("SWNPT" for brevity) having a generally quadrilateral silhouette (or toroidal, if the side web is capped to mimic the sidewall of a pneumatic tire, and the ribs are extended appropriately), viewed in cross-section in a vertical plane through the tire's (and wheel's) rotational spin axis. In one embodiment the cross-section is a generally rectangular silhouette, in another embodiment, one or both sides of the silhouette are either angulated or arcuate, and in yet another, a hybrid of the preceding rectangular and angulated or arcuate silhouettes. The tire comprises angularly oriented, oppositely directed planar rib members (referred to as "crossed ribs") integrally connected by a single planar web member on one side of the tire ("side web" for brevity) which results in a non-expansible annular honey-comb sandwiched between inner and outer hoop members ("hoops") so that there is at least one row of passages having a cross-section generally resembling a quadrilateral. This and other rows of passages which may have the same, or different, cross-sectional shapes are formed as in a honeycomb, by the crossed ribs. All passages are open at the passages' open ends away from the side web (hence referred to as "one-side-open" honeycomb construction). By "non-expansible" we refer to the diameter of a wheel fitted with a NPT, which diameter does not get larger when the wheel is rotated, due to the centrifugal forces generated during operation.
The SWNPT of this invention is configured from an elastomeric synthetic resinous material having specified desirable properties, so as to provide optimum handling, cornering and load bearing characteristics for a given mass of resinous material. The term "handling" is used to define the general responsiveness of the vehicle to the expectations of the driver, but more specifically refers to the dynamics of the tires on the wheels of the vehicle, and in turn, the vehicle itself, due to lateral acceleration. By "elastomeric synthetic resinous material" or "elastomer" we refer to a stiff, resilient, material having specific characteristics defined hereinafter. The elastomer may contain a minor proportion of a homopolymer or copolymer of a conjugated diene, preferably less than 10% by weight, and more preferably none. Rubber, whether natural or synthetic (particularly, styrene-butadiene rubber, SBR), and blends thereof containing a major proportion by weight of a homopolymer or copolymer of a conjugated diene, whether vulcanized or not, is not an elastomer as defined herein, as it fails to meet the criteria set forth herebelow.
In particular, the SWNPT provides handling and cornering comparable to that provided by the rectangular nonpneumatic tire ("RNPT") with a central web, disclosed in U.S. Pat. Nos. 4,784,201 and 4,832,098. Either nonpneumatic tire "NPT" (as used herein the acronym NPT refers to either a RNPT or a SWNPT, or both) allows itself to be deformed due to compression, and reverts to its original cylindrical shape while carrying its share of a load, typically as a tire mounted on a wheel rim of an automobile or a motorcycle. The dynamics of such deformation under load determines whether handling is satisfactory or not, such judgment generally being made with respect to a conventional pneumatic tire. Of course, a pneumatic tire has sidewalls which are smoothly and continuously blended into both side edges of its tread.
When a pneumatic tire is severely deflected laterally in the inboard direction, the portion of the sidewall nearest the outboard edge of the tread may come into contact with the road. By "inboard direction" we refer to the direction in which the vehicle is being turned. With greater deflection, as in a tighter turn at higher speed, progressively more of the sidewall contacts the road. Under the severest conditions, the identifying lettering on the sidewall may be scuffed away by abrasion with the road surface. The side web, positioned on the outboard edge, counters such lateral deflection in the SWNPT.
A RNPT, specifically, exhibits marginally satisfactory handling when the RNPT is used under conditions which generate a high lateral acceleration. Under such dynamic conditions, the annular portion of the RNPT in contact with the road, is deflected laterally without benefit of any restraint by its sidewalls, because the RNPT doesn't have any. It will be recognized that the tread of a NPT comes to an abrupt end at each of its shoulders. Under severe cornering conditions, the outboard edges of the tread of the RNPT are severely abraded.
The unique coaction of the structural elements of the SWNPT, distributes forces, particularly those generated during turns, so that the forces are redirected by the presence of its outboard side web. Such redistribution of the forces unexpectedly provides the SWNPT with essentially the same or better deformation and load-bearing characteristics than those of a RNPT having the same mass. Though the ride provided by each belies the stiffness of the elastomeric material and the total lack of air trapped within, the outboard side web provides a unique handling advantage over a pneumatic tire on a passenger automobile, yet with substantially no noticeable loss of the high degree of comfort provided by the pneumatic tire. The outboard sidewall of a pneumatic tire does not provide the same distribution or degree of stiffness provided by the side web.
The unique one-side-open construction of the SWNPT effectively dissipates heat generated during continuous cycling between alternating compressive and tensile forces in play during operation. Like the RNPT, the SWNPT is ideal for a wide spectrum of wheeled vehicles in which (i) the susceptibility to puncture is obviated, (ii) increased wheel diameter is desirable, and (iii) progressive failure of the SWPT is required. This last condition applies to special-purpose vehicles such as a personnel carrier subject to sudden and serious damage, as for example a bullet, so that the effect of such damage is thus minimized.
The overriding advantage of a pneumatic tire is the cushioning it provides, which cushioning, to date, as far as we know, has not been effectively mimiced with other NPTs. The disadvantage of the pneumatic tire is its susceptibility to being punctured. We know of no construction for an elastomeric NPT, other than the RNPT disclosed in the aforementioned commonly assigned patents, or of any prior art SWNPT which is reliable and rugged enough to withstand the rigors of normal operation when mounted on the wheel of an automobile.
As will readily be realized, NPTs have been routinely used on vehicles where neither handling, nor cushioning the load is a prime consideration, as for example in fork lift trucks, carts, wheelbarrows, tricycyles, and the like. Even so, the use of NPTs in such applications was less than satisfactory because prior art NPTs had undesirable handling characteristics. In addition, one could not provide a variable spring rate in a prior art NPT without changing either its design, that is, its structural configuration, or the materials of its construction. Apart from the lack of "good ride quality", solid tires, in particular those made from vulcanized rubber, were subject to high heat buildup and subsequent degradation after only constricted usage over a severely limited period. No prior art NPT that we know of suggests an integral NPT with a single side web and crossed ribs which are able to deform locally, that is, near the point where the NPT contacts the surface on which it is run, yet discharges its load-bearing and cushioning functions in a manner analogous to that in which a pneumatic tire discharges such functions.
In European patent application No. 0159888 A2, published Oct. 30, 1985, one embodiment (FIG. 9) of a honeycomb structure is provided, but with dual planar side webs which enclose planar ribs adhesively secured so as to cross each other in the central circumferential plane, therefore not forming a honeycomb structure (requiring intersection of the ribs along the entire length of each rib) sandwiched between two sidewalls. Moreover, though the dual sidewalls provide desired support and rigidity, the structure is a pneumatic tire which cannot be cooled because air is enclosed in an air-tight annulus. The open construction of our SWNPT not only serves to cool it during operation, but permits superior handling in the corners.
The concept of providing a web in a solid rubber tire is old, having been taught in German Offenlegungsschrift No. 24 60 051. For additional strength, the upper and lower flanges of the I-beam-like member are connected with interdigitated sinusoidal scallops along its inner surface. This manner of strengthening the structure is different from the oppositely directed ribs on either side of the web of the NPT. This reference, and all prior art references failed to recognize the peculiar function of planar oppositely directed angulated ribs which are undercut to help ensure that bending is negated, so that, instead of bending, buckling occurs when the critical load is exceeded. It is this peculiar characteristic of compressive deformation of the SWNPT in normal use, coupled with buckling of the ribs when the critical load is exceeded, which is instrumental in giving the SWNPT `ride` characteristics which mimic those of a pneumatic tire, and excellent handling characteristics.